CURRENT RESEARCH CONCERNS: (1) Evidence for a 2-photon reaction in the photoenzymatic repair of UV-irradiated Haemophilus transforming DNA in vitro and its relation to the activation of photoreactivating enzyme by preillumination; (2) Inhibition of recombinational (or "post-replication") repair by streptomycin in E. coli mutants resistant to low levels of streptomycin; (3) Characterization of a third UV repair system in phage T4. FUTURE RESEARCH: (4) The role of E. coli DNA polymerase I in host-cell reactivation of phage T1; and (5) Comparison of wildtype and UV-sensitive mutants of E. coli regarding the extent of photorepair (by sunlight) of UV damage concurrently caused by sunlight. BIBLIOGRAPHIC REFERENCES: W. Harm: Analysis of photoenzymatic repair of UV lesions in DNA by single light flashes. X. Stability of the photoreactivating enzyme in resting Escherichia coli cells. Mutation Res. 34, 69-74 (1976). Tom Chiang and W. Harm: On the lack of host-cell reactivation of UV-irradiated phage T5. I. Interference of T5 infection with the host-cell reactivation of phage T1. Mutation Res. 36, 121-134 (1976).